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What “resume” means

After a successful login, the server returns a resume block in login_ok: 
{
  "resume": {
    "serverEpoch": "0804ab61513c4681a3afd8afc1fb2f75",
    "resumeWindowMs": 3000,
    "replayChannels": ["fixtures", "scores"],
    "serverEntryIds": {
      "fixtures": "1766414833582-2542",
      "scores": "1766418736962-198"
    }
  }
}
This tells you:
  • serverEpoch — identifies the current gateway session (changes on restart)
  • resumeWindowMs — how long replayable data is buffered
  • replayChannels — channels eligible for replay
  • serverEntryIds — server’s latest cursor per channel

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What clients must persist

To resume safely, persist:
  1. serverEpoch
  2. The most recent entryId you processed per channel
{
  "scores": "1766418736962-198",
  "fixtures": "1766414833582-2542"
}

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entryId format

Each streamed message includes an entryId: 
<ts_ms>-<seq>
  • ts_ms — server timestamp (UTC, milliseconds)
  • seq — monotonic per-channel sequence
Important:
  • entryId is a cursor, not a delivery guarantee
  • Gaps are normal (upstream behavior, coalescing, backpressure)

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Resume login example

On reconnect, send the same serverEpoch and your stored cursors: 
{
  "type": "login",
  "apiKey": "YOUR_API_KEY",
  "channels": ["fixtures", "scores", "odds"],
  "serverEpoch": "0804ab61513c4681a3afd8afc1fb2f75",
  "lastSeenId": {
    "scores": "1766418736962-198"
  }
}
If replay succeeds, the server sends: 
{
  "type": "resume_complete",
  "serverEpoch": "0804ab61513c4681a3afd8afc1fb2f75"
}

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snapshot_required (when replay is not possible)

Sometimes replay cannot be done safely. In that case the server sends: 
{
  "type": "snapshot_required",
  "reason": "resume_window_exceeded",
  "channels": ["scores"],
  "serverEpoch": "0804ab61513c4681a3afd8afc1fb2f75",
  "resumeWindowMs": 3000,
  "serverEntryIds": {
    "scores": "1766418738000-220"
  }
}

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Possible reasons

  • server_restarted — gateway restarted, cursors invalid
  • resume_window_exceeded — your cursor is older than the replay buffer
  • client_backpressure — your client couldn’t consume replay fast enough

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Important nuance

Replay eligibility depends on cursor age, not disconnect duration: 
(now_ms - last_seen_entry_ts_ms) > resumeWindowMs
⇒ snapshot_required is likely
A very short disconnect can still exceed the window if your last processed message is already old.

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How clients should handle snapshot_required

When you receive snapshot_required:
  1. Fetch a fresh snapshot via REST for the listed channels (e.g. /fixtures, /fixtures/odds, /futures)
  2. Clear lastSeenId for those channels
  3. Continue processing live updates
The gateway continues streaming after snapshot_required. This message is your signal that local state must be rebuilt.

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Python reconnect example (FULL TEMPLATE)

This example:
  • Persists serverEpoch and per-channel lastSeenId
  • Sends cursors only for replayable channels
  • Handles snapshot_required
  • Automatically reconnects on failure
import asyncio
import json
import time
import websockets

WS_URL = "wss://v5.oddspapi.io/ws"
API_KEY = "YOUR_API_KEY"

server_epoch = None
replay_channels = None
last_seen = {}

async def run_once():
    global server_epoch, replay_channels, last_seen

    async with websockets.connect(
        WS_URL,
        ping_interval=20,
        ping_timeout=20,
        max_size=4194304
    ) as ws:
        login = {
            "type": "login",
            "apiKey": API_KEY,
            "channels": ["fixtures", "scores", "odds"],
            "receiveType": "json",
        }

        # Resume mode
        if server_epoch:
            login["serverEpoch"] = server_epoch

        # Only send cursors for replayable channels
        if replay_channels:
            cursors = {
                ch: eid
                for ch, eid in last_seen.items()
                if ch in replay_channels
            }
        else:
            cursors = dict(last_seen)

        if cursors:
            login["lastSeenId"] = cursors

        await ws.send(json.dumps(login))

        async for raw in ws:
            if isinstance(raw, (bytes, bytearray)):
                raw = raw.decode("utf-8", errors="replace")

            msg = json.loads(raw)
            msg_type = msg.get("type")

            if msg_type == "login_ok":
                resume = msg.get("resume") or {}
                server_epoch = resume.get("serverEpoch") or server_epoch

                rc = resume.get("replayChannels")
                if isinstance(rc, list):
                    replay_channels = set(map(str, rc))

                continue

            if msg_type == "snapshot_required":
                channels = msg.get("channels") or []
                for ch in channels:
                    last_seen.pop(ch, None)

                # Trigger REST snapshot refresh here
                print("Snapshot required for:", channels)
                continue

            if msg_type == "resume_complete":
                print("Resume complete")
                continue

            # Data message
            channel = msg.get("channel")
            entry_id = msg.get("entryId")

            if isinstance(channel, str) and isinstance(entry_id, str):
                last_seen[channel] = entry_id

async def main():
    while True:
        try:
            await run_once()
        except Exception as e:
            print("Disconnected:", e)
            await asyncio.sleep(1)

asyncio.run(main())